New iPhone. Rep told me to update phone and factory reset it

Hello. Today I financed an iPhone for my wife at an Experience Store. We aren't trading anything in or adding a line. After paying the taxes and fee to turn the device on, the rep tells me that when I set up the new iPhone, I need to update it to the latest iOS and then do a factory reset, because if we don't, the transfer from her old iPhone and the new one might go "wrong".

I'm an Android guy, so I wouldn't know much about iPhones and iOS in general, but this sounds like a step that's unnecessary.

But like I said, I don't know much about iPhones so perhaps this is correct?

Edit: She updated and transferred over everything seamlessly. Thanks for all the help!!